1. Field of the Invention
This invention relates to a filter and, more particularly, to a filter having replaceable filtering material.
2. Description of the Prior Art
Japanese Unexamined Practical Idea Publication No. 3-46812 discloses a prior art filter.
As shown in FIG. 13, this filter includes a case 1 having a cup-shaped body and a flange 2 which extends radially from the outer periphery of the body proximate the open end of the body. A cover 3 covers the open end of the case 1. The cover 3 includes a tubular portion 4, the inner diameter of which is sized to receive the open end of the case 1. The tubular portion 4 constitutes a male portion on which a screw thread is formed.
An annular fastener 5 has an L-shaped cross section constituted by a cylindrical portion 6 and a retainer 7. A screw thread screwable to the male thread of the tubular portion 4 is formed at the inner peripheral surface of cylindrical portion 6, whereby the cylindrical portion 6 constitutes a female portion of the fastener. The retainer 7 extends from the end of the cylindrical portion 6 toward the center of the fastener 5. The inner diameter of the cylindrical portion 6 is larger than the outer diameter of the case taken at the flange 2, and the inner diameter of the retainer 7 is smaller than the outer diameter taken at the flange 2 but larger than the outer diameter of the cup-shaped body of the case. A filtering material 8 is housed within the case 1.
When the case 1 and cover member 3 are to be secured, an O-ring 9 is disposed on the flange 2 of the case 1, and the open end of the case 1 is inserted into the tubular portion 4 of the cover 3. Next, the fastener 5 is fitted over the case 1 whereupon the case passes through the cylindrical portion 6 and retainer 7. The screw thread formed on the inner periphery of the cylindrical portion 6 and the screw thread formed on the outer periphery of the tubular portion 4 are screwed together by rotating the fastener 5 in one direction. When so tightened, the retainer 7 contacts the flange 2, becomes integrated with the cover 3, and pulls the case 1 into the cover 3.
When the case 1 is to be removed, the fastener 5 is rotated in the opposite direction.
In the above-described prior art filter apparatus, if the case 1 is supported and the fastener 5 is rotated, the cover 3 tends to rotate together with the fastener 5, whereby it is not possible to secure the cover 3 tightly to the case 1. In particular, when the cover 3 has a generally overall planar configuration and a threaded hole formed at the center thereof, and an attempt is made to screw a threaded portion protruding from an engine into the threaded hole, as in an automotive oil filter, the cover 3 will slip. Therefore, it is difficult to secure the cover 3 to the engine.